This invention relates to a method of, and an apparatus for, producing a trigger signal in accordance with the occurrence of an event occurring in an almost periodic manner within periodically consecutive time intervals and having a specific distinguishing feature relative to the remainder of the events occurring within each of said time intervals.
In particular applications, a trigger signal is required dependent on the occurrence of an event the significance of which is not recognised immediately on its occurrence and is only recognised at a later stage, for example at the end of the relevant time interval. For example, where a trigger signal is required to be produced on the last pulse of a series of pulses the number of which varies or for the highest amplitude pulse of a series of pulses of varying amplitude it is only possible to determine at the end of the train of pulses or at the end of the relevant time interval which pulse was destined to produce the trigger signal.
Known apparatus for producing a trigger signal of the above-mentioned type are thus only able to produce the trigger signal at the end of a specific delay following the occurrence of the relevant event. For example, the duration of a mainly periodically repeating pulse train has been determined by causing the individual pulses to enable a counter and transferring the output of the counter to a memory at the end of each individual pulse whilst permitting the counter to continue counting during the pauses between the pulses. At the end of the relevant time interval the memory then contains a value which corresponds to the duration of the pulse train.
In addition to the delay in producing the trigger signal indicating the end of the pulse sequence following the end of the pulse sequence, a disadvantage of this known apparatus is that the transfer of the output of the counter to the memory cannot be carried out with sufficient speed in many cases thereby limiting the operating frequency of the apparatus.
It is accordingly an object of this invention to provide a new or improved method of and apparatus for producing a trigger signal in which the above-mentioned disadvantages are overcome or reduced.